The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, in an automatic transmission field, a research of a multistage of gear shifts has been performed to reduce fuel consumption and improve drivability of a vehicle.
The multistage of gear shift stages of such an automatic transmission is desired to increase a power performance and driving efficiency while downsizing an engine.
However, as a gear shift stage increases, the number of components of an automatic transmission increases and thus a mounting capability, a cost, a weight, and transfer efficiency are undermined.
Therefore, in order to increase a fuel efficiency through a multistage, a planetary gear train has been developed to enhance power efficiency with reduced components.
Nowadays, an 8-speed automatic transmission has been developed to implement gear shift stages of an 8-speed or more by utilizing a planetary gear train.
However, we have discovered that, in an 8-speed automatic transmission, because a shift span of a gear shift ratio (a factor for securing linearity of interstage ratios) is maintained in a level of 6.5-7.5, an enhancement effect of a power performance and fuel consumption with a downsized engine is below a desired level of efficiency.
Further, when a shift span rises to a level above 9.0, the 8-speed automatic transmission is disadvantage in securing linearity of the ratios between gear shift stages (i.e., interstage ratios).
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.